Ultrasonic transducers, particularly those used in industrial applications, typically have to meet certain minimum safety requirements and standards. Such requirements include protection from flying particles and inadvertent or accidental impacts, resistance to corrosion from liquids to be contacted, chemical inertness so as not to contaminate the liquid to be measured, a wide range of tolerance to static or dynamic pressure variations, and/or a wide range of operational or storage temperatures.
Current solutions for protecting ultrasonic transducers include the addition of a protective layer, such as a metallic protective layer, attached generally to the front of a piezoelectric element of the transducer. In these structures, acoustic wave reflections arise at two locations. A first reflection occurs generally at a boundary between the protection layer and a bonding layer. A second reflection also occurs at a boundary between the protection layer and radiation medium. The two distinct locations of these reflections result in a sharp resonant peak, reduced sensitivity and ringing of the received signal.
Moreover, ultrasonic transducers often utilize various forms of acoustic impedance matching solutions or acoustic impedance converters. These may include single or multiple layer structures of polymer and/or metal materials. In particular, acoustic impedance converters may utilize one or more one-quarter (¼, or “quarter”) wavelength thick layers for providing a desired acoustic impedance conversion. Moreover, acoustic impedance converters may utilize relatively thin metal and polymer layers on the order of, for example, one-thirty seventh ( 1/37) and one-sixteenth ( 1/16) of a wavelength in thickness, respectively, for achieving acoustic impedance conversion. These converters lack suitability as protective structures due to the minimal thickness of their metal layers. Moreover, as their metal and polymer layers are configured (e.g. sized) to function cohesively as an impedance converter having targeted characteristics, altering the thickness of the metallic layers for improving protection would lead to degraded intended performance.
Improved structures offering suitable protection, chemical inertness and resistance to thermal degradation and/or fatigue, as well as improved sensitivity and wideband operation of the transducer are desired.